The invention relates to a tool for the metal-cutting machining of a surface, such as a valve seat in a cylinder head of an internal combustion engine and particularly to the configuration and attachment of the cutting tip thereof and relates to a method for the metal-cutting machining of such surface, such as a valve seat in a cylinder head of an internal combustion engines.
Tools and methods of the type under discussion here are known. The tools have a cutter tip which comprises at least one geometrically defined cutting edge. With the aid of that edge, chips can be removed from the valve seat either by the tool being rotated with respect to a fixed workpiece or the workpiece being rotated with respect to a fixed tool. As a rule, the former of the two procedures is performed. The valve seat has a first annular surface which encloses, with reference to an imaginary central axis of the annular surface, a first angle of inclination of, for example, approximately 45°. The first annular surface essentially determines the gas tightness of the valve. The first surface is adjoined first by a second annular surface with an angle of inclination of approximately 15° and secondly by a third annular surface with an angle of inclination of approximately 75°. During the machining of the valve seat, the tool is displaced axially along the common central axis of the annular surfaces until the cutter tip is in engagement with the valve seat and, for example, the first annular surface is machined. The machining therefore takes place by movement of the tool in the direction of the valve axis, which coincides with the central axis of the annular surface. The machining is referred to as a valve-cutting process. Preferably, the tools selected can be used to machine surfaces like both the valve seat and the valve guide, i.e. they have a cutter tip for machining the valve seat and a reamer for machining the valve guide. As a result, the central axis of the valve seat is aligned very precisely with the central axis of the valve guide, which contributes to the valve being well sealed.
The valve seat in cylinder heads of internal combustion engines is generally realized by valve seat rings which consist of very hard, wear-resistant sintered materials, which means that the machining is very complex and cubical boron nitride (CBN) generally has to be used, which is very expensive. In addition, very exacting requirements are made of the quality in order to ensure the “gas tightness”. Even a small amount of wear to the cutting edge leads to the permissible tolerances being exceeded. Overall, it turns out that the costs for machining the valve seat are very high.